Burner control



Dec. 15,1942. J, M WILSQN 2,305,501-

BURNER CONTROL Filed Sept. 28, 1940 INVENTOR John M. Wilson...

ATTORN EY Patented Dec-15,1942

BURNER CONTROL John M. Wilson, Minneapolis, Minn., minor to Minneapolis-Honeywell ,Begulator Company, Minneapolis, Minn, a corporation of Delaware Application September 28, 1940, Serial No. 358,791 14 Claims. '(ci. 158-28) The present invention relates to apparatus for, and a method of, controlling a burner circuit. More particularly the invention embraces a novel burner control which utilizes a Wheatstone bridge including a resistance which is heat responsive to detect the flame withinthe furnace or other heating device. 7

An-object of this invention is to provide a simplified burner control which has no moving parts subjected to destructive conditions to thereby obtain a high degree of safety.

Another object, in connection with the preceding object,'is to provide such a control utilizing a Wheatstone bridge as a combustion detector, and a safety switch heater connected across the Wheatstone bridge in a manner so that it will respond to a plurality of predetermined condi-.

tions.

A further object, in connection with the above objects, is to provide a controller using a Wheatstone bridge in which one leg is responsive to combustion conditions and in which the other leg is heated by an electrical heater that is energized in response to a demand for heat.

Another object is to provide a Wheatstone bridge burner control circuit which is opened and no power is consumed when there is no demand for heat.

The above and other objects will become apparent upon consideration of the accompanying specification, the appended claims, and the drawing, the single figure of which diagrammatically illustrates a burner control circuit includn my invention. I

a A burner controller it which may take the form or a burner motor, a fuel delivery pump, a fuel valve, or similar device, and an ignition device II are electrically controlled by a condition responsive means i2. The condition responsive member may take the form of a thermostat composed of bimetal l3 which carries a flexible contact arm I3 and a relatively stiff contact arm IS. The contact arm ll cooperates with a'stationary contact l3 and the contact arm I5 cooperates with a stationary contact H. The contact l6 engages arm I! prior to engagement'of arm l5 and contact I! when the-device is cooled.

A relay mechanism 23 is controlled by the condition responsive means I2. The relay may take the form of a conventional relay coil 2| which moves contact arms 22 and 23. Current for the relay 23 is furnished from a transformer 25 which has a low voltage secondary 26 and a high voltage primary 21.

A safety switch mechanism 30 is provided and controls the electric circuit to all of the mechanism of the system. The safety switch comprises a suitably mounted first contact blade 3| and a second contact blade 32 which is inherently biased away from the blade 3|. These two contact blades 3| and 32 carrycontacts 33 and 34, respectively. The contacts are latched into ongaged position against the. bias of blade 32 by a thermal member 35. when the thermal mem-' her is in the cold position shown, the upper end 36 thereof is beneath the contact blade 32 to maintain the contacts 33 and 34in engagement. When the thermal element 35 is heated to a predetermined degree the upper end-3i thereof will move to the left from beneath the contact blade 32, thus permitting the contacts 33 and 34 to separate. A conventional trip-free resetter is indicated at 31. When the thermal 'element 35 moves from beneath the blade 32, said blade will engage the reset button 33 and the other blade 3| will engage the button 33. The buttons 38 and 39 maintain the blades 3| and 32 in spaced relationship thus separating the contacts 33 and 34. A heater III is located adjacent the thermal element 35 and operates in a manner to be hereinafter more fully described.

An energizing circuit for the transformer 25 may be traced as follows: from line wire 35 which leadsto a suitable source of power, not shown, through the conductor 41, the safety switch 30, wire l3, primary 2'] of transformer 25, and conductor 33 to the other line wire 46.

A combustion responsive means 63 takes the form of a Wheatstone bridge having resistances SI, 62, 63, and 64 which may have substantially identical resistivity for a given temperature.

The resistances ii and 32 are preferably adapted to vary similarly in resistivity upon being heated at substantially the same rate and level off in resistivity at substantially the same temperature and ohmic resistance values, for example at 600 degrees Fahrenheit. The supply conductor for the Wheatstone bridge may lead from the relay contact arm 23 through conductor 35 and conductor. A second conductor 61 connects the Wheatstone bridge to the line wire 4 and is connected between the two resistances 3 and i4.

The resistance it is affected by a heater l0. Whenever the relay 23 is energized an energizing circuit therefor leads from the relay arm 23, wire 35, wire ll, heater ll, wire 12, and adjustable resistance I3, and a wire II to the other line wire 35.

The resistances 3| and 32 are made of a metal which has the characteristic ofv varying its reposition.

sistivity upon a change in temperature. For example, the metal might be nickel or some other compound in which the resistance of the element is raised when subjected to a higher temperature. The two resistances 5| and 52 are subjected to different conditions, the resistance 6| being afiectedby the heater T and the resistance 62 being affected by radiant heat produced by the flame 15 of the burner which is indicated in broken lines. When resistances GI and 62 are at substantially the same temperature the potentials of points A and B are the same and therefore the bridge is in balance. When one or the other of the resistances is changed, the potential of one of points A or B will be varied with respect to the other and the bridge will be in an unbalanced condition.

The safety switch heater 40 is connected across points A and B by the conductors 80 and 8| and therefore whenever the bridge is unbalanced, current will flow through heater 40.

Operation of the device A circuit for the fuel delivery means ill and the ignition means II is as follows: from conductor 45, wire 41, safety switch 30, wire 50, contact of the relay 2|], contact arm 23, conductor 52, conductors 53 and 54, to the fuel delivery means and the ignition means, and conductors 55 and 56 to the other line wire 46.

'By tracing the above circuit it will be noted that when the relay 2D is energized because of the closure of the contacts of the condition responsive element |2 a circuit is established for the fuel delivery means and the ignition means. At the same time, there will be a circuit established for a combustion responsive means generally indicated by the reference character 60.

The thermostat I3 is shown in its satisfied Assuming now that the temperature falls, the contact arms l4 and I5 will be moved towards the right. The contact arm M will first engage the contact arm l6. However at this time, the relay 2!! will not be energized because the contact arm 22 will not have engaged the contact 85. Upon a further decrease in temperature the contact blade l4 will flex to permit engagement of the contact arm IS with the contact I1. At this time a circuit will be established for the relay coil 2| which may be traced as follows: from the secondary 26 of the transformer 25 through the wire 80, contact |5, contact arm I4, bimetal l3, contact arm l5, contact l1, wire 9|, relay coil 2|, and wire 92 to the other side of the secondary 26 of the transformer. This circuit will cause the relay to be pulled in and the contact arms 22 and 23 will engage their respective contacts 85 and 5|, respectively. A holding circuit for the relay 2| may, be traced as follows: from the secondary 26, wire 90, contact l6, contact arm l4, bimetal l3, wire 95, contact 85, relay contact arm 22,

wire 86, relay coil 2|, and wire 92 back to the other side of the secondary 25. It is seen then that a circuit is provided wherein a thermostat diiferential is obtained in that contacts l5 and IT must be engaged to pull in the relay but the relay will be held in independently of the contact H. In other words, the relay will not again drop out until the contact M has separated from the contact l6 thereby providing a temperature differential.

With the relay 20 energized, the fuel deliv-.

ery means |0-and the-ignition means II will be relay switch arm 23 through the circuit previously traced. Simultaneously, with such energization the Wheatstone bridge will also be energized as well as the circuit to the heater 10 which heats the resistance SI of the Wheatstone bridge 60.

Assume now that combustion does not properly take place. With the heater l0 energized, heat will be supplied to the resistance 5|. When the resistance 6| is heated the resistivity thereof rises and the bridge will therefore be unbalanced between the points A and B. Therefore there will be a current impressed across the safety switch heater 40 and after a predetermined time, for example 90 seconds, the upper end 36 of the thermal timer will move from beneath the blade 32 and permit the contacts 33 and 34 to separate, thus deenergizing the burner circuit as well as the circuit to the Wheatstone bridge 60.

If combustion takes place propely upon energization of the circuit to the Wheatstone bridge 60, the resistor 62 will be heated by the flame. It is preferable to have the resistance 62 heat up at substantially the same rate as the resistance 5|. Then, because these two resistances have substantially the same resistivity to temperature coefiicients, there will be no unbalance of the Wheatstone bridge and no current will be impressed across the heater for the safety switch 30. Therefore it is seen that a combustion detector is provided which operates upon energization of a burner circuit for immediately detecting the presence of flame. Also it is seen that if combustion does not occur the safety switch will be opened, but if combustion does take place properly the safety switch will not be operated.

Assuming that the burner has started up and has been operating normally as set forth in the preceding paragraph and a flame failure occurs. Previous to this time the resistances BI and 62 will be at substantially the same temperature so that the bridge is balanced and the heater 40 is inoperative. However, when the flame failure occurs the resistance 62 will very rapidly cool off energized through the safety switch 30 and the which unbalances the bridge and causes current to flow through the heater 40 to heat the thermal member 35 and unlatch the safety switch 30 after a predetermined time interval. The switch 30 must then be reset manually before the burner can be restarted.

In the event that any of the resistances 6|, 62, 63 or 64 burn out, the Wheatstone bridge would be greatly unbalanced and as a result of the energization of the heater 40 the safety switch 30 would be moved to open position. If the heater 10 or the resistance 13 were burnedout, the safety switch would be opened upon the occurrence of normal combustion. Also by the present'novel arrangement the heater 40 may be of low ohmic resistance and hence perfectly safe against burning out.

It is seen that I have provided a safety switch in combination with a Wheatstone bridge wherein different legs of the bridge are subjected to different predetermined conditions. Although I have shown and described one form that my invention may take, it will be clearly understood that many other modifications embodying the principle of the instantdevice will occur to those skilled in the art, therefore it is to be understood a pair of resistances which change their resistivity upon a change in temperature, a heater for one of said resistances controlled by said control means, said other resistance being affected by the flame produced by the burner, and connecting means between said two resistances andv said switch actuator for causing said resistances to control said switch actuator.

2. In a fuel burner system, in combination, a

burner motor, a circuit therefor, a condition re-' sponsive controller in control of said circuit, a safety switch also in control of said circuit, a

switch actuator including a heater associated with said safety switch for actuating the same,

a pair of resistances which change their resistivity upon a change in temperature, a heater for one of said resistances controlled by said control means, said other resistance being affected by the flame produced by the burner, and connecting means between said two resistances and said switch actuator for causing said resistances to control said switch actuator.

3. The combination with a fuel burner system comprising a burner motor, a controller, a thermal safety switch, and a burner motor energizing circuit controlled by said controller and said safety switch; of a Wheatstone bridge having a plurality of resistance legs which change in resistivity upon a changein temperature, and a heater for said safety switch connected across said bridge, one of said legs being subjected to a first controlled heat condition to vary the re'sis tivity thereof, and at least one other of said legs being subjected to a second heat condition caused by the operation of said burner motor to vary the resistivity thereof.

4. The combination with a fuel burner system comprising a burner motor, a controller, a thermal safety switch, and a burner motor energiz ing circuit controlled by said controller and said safety switch; of two parallel resistance circuits controlled by said controller and subjected to different predetermined heatconditions to vary the resistivity thereof, a heater for said safety switch joined across intermediate points in said resistance circuits in a manner so that it will respond in accordance with the temperature differential between said circuits, and means controlled by said controller to cause a temperature difierential when said burner motor energizing circuit is en- 5. The combination with a fuel burner system comprising a burner motor, a controller, a thermal safety switch, and a burner motor energizing circuit controlled by said controller and said safety switch; of a Wheatstone bridge having two parallel resistance circuits including two resistors which change their resistivity upon a change in their temperatureand two flxed resistances in series therewith to form a'pair of intermediate bridge junctions, an electric heater for said safety switch connected between said junctions,

and means for difierentially heating said resistors tothereby impress a current across said heater to cause operation of said safety switch.

6. The combination with a fuel burner. system comprising a burner motor, a controller, a therform a pair of intermediate bridge junctions, a-

first heater controlled by said controller for supplying heat to one of said resistors tounbalance said bridge when said circuit is energized, the

other of said resistors being responsive to the flame of the burner to rebalance said bridge, and a second heater for affecting said safety switch connected across said bridge and being responsive to the unbalanced condition thereof.

7. The combination with a fuel burner system comprising a burner motor, a controller, a thermal safety switch, and a connecting circuit; of a Wheatstone bridge having two parallel resistance circuits including two resistorsv which change their resistivity upon a change in temperature and two fixed resistances in series therewith to form a pair of intermediate bridge junctions, a first heater controlled by said controller for supplying heat to one of said resistors to unbalance said bridge when said circuit is energized,

the other of said resistors being responsive to the fect thereof upon said one resistor to thereby modify the operation of said second heater.

8. In a fuel burner system, in combination, electrical fuel delivery means, igniting means therefor, an electrical circuit for said delivery and igniting means, a control switch for energizing and deenergizing said circuit in response to variations in a variable condition, control means for also controlling said circuit, timing means associated with said control. means, a plurality of resistance circuits, said timing means being associated with said circuits in a manner so as to respond to the diiference of resistivity therebetween, and means controlled by said control switch for affecting one of said resistance circuits to vary the resistivity thereof to effect operation of said timing means, another of said resistance circuits being reponsive to the heat of combuslion eifected by said fuel delivery means to thereby compensate said one resistance circuit to render said timing means inoperative.

9. In a fuel burner system, in combination electrical fuel delivery means, igniting means therefor, an electrical circuit for said delivery and igniting means, a control switch for energizin and deenergizing said circuit in response to varia-. tions in a variable condition, control means for also controlling said circuit, timing means 'associated with said control means, a Wheatstone bridge comprising a plurality of heat responsive legs that change their resistivity, a heater in said circuit, one of said legs being varied in resistivity by said heater atapredetermined rate upon energization of said circuit and another of said legs being varied in resistivity by the heat'of combustion caused by said fuel delivery means, and means connecting said timing means across said bridge in a manner so as to respond to an unbalanced condition of the bridge.

10. In a fuel burner system, in combination, a burner provided with igniting means, a control circuit therefor, a control switch for energizing and deenergizing said circuit in response to variations in a variable condition, a safety switch for also controlling said circuit, thermal timing means associated with said safety switch, a Wheatston bridge comprising a plurality of legs that change their resistivity upon a change in temperature, said timing means being connected across said bridge in a manner so as to respond to an unbalanced condition of the bridge, and a with the energization of said circuit for heating one of said legs to thereby unbalance said bridge to cause energization of said thermal timing means, another 01' said legs being responsive to the heat of combustion eiiected by said burner to rebalance said bridge if combustion properly takes place to thereby effectively deenergize said thermal timing means.

11. The combination with a fuel burner system comprising a burner motor, a controller, a safety switch, and a circuit means including said controller and safety switch for controlling said burner motor; of a Wheatstone bridge having a pair of resistors and a pair oi intermediate bridge Junctions, means controlled by said circuit means for changing the resistance of one of said resisters to unbalance said bridge, another of said resistors being responsive to the flame of the burner to rebalance said bridge, and a safety switch actuator connected to said junctions and being responsive to the unbalance of said bridge to operate said safety switch.

12. The combination with a fuel burner system comprising a burner motor, a controller, a safety switch, and circuit means including said controller and said safety switch for controlling said burner motor; of an electrically operated safety switch actuator, a pair of resistors which change their resistivity upon a change in temperature,

means controlled by said circuit means for changheater adapted to be energized simultaneously ing the temperature of one of said resistors, said other resistor being heated by the flame oi the fuel burner, and connecting means between said two resistors and said switch actuator for causing said resistances to control said switch actuator.

13. The combination with a fuel burner system comprising a burner motor, a controller, a safety switch, and circuit means including said controller and said safety switch for controlling said burner motor; of an electrically operated safety switch actuator, a pair of resistors which change their resistivity upon a change in temperature, connecting means between said pair of resistors and said switch actuator, and means in said circuit means controlled by said controller for varying the temperature of one of said resistors for causing electricity to be impressed upon said actuator, the other 01 said resistors being responsive to fuel combustion to reduce the amount of electricity supplied to said actuator upon the occurrence of a flame.

ii. The combination with a burner and an en ergizing circuit therefor, of control means responsive to a controlled condition for closing said circuit to render said burner operative, 2. Wheatstone bridge also controlled by said control means and energized when said means closes said circuit, means also controlled by said control means for affecting one leg means of said bridge to vary its resistance andunbalance the bridge, said bridge being rebalanced by another leg means responsive to the occurrence of a flame, a switch actuator connected across said bridge, and a switch also in control of said circuit, said switch being actuated by said actuator in response to the condition of balance of said bridge.

JOHN M. WESON. 

